Sandrine Gomes’s research while affiliated with University of Clermont Auvergne and other places

Iron-doped hydroxyapatite (Fe-HAp) is regarded as a promising magnetic material with innate biocompatibility. Despite the many studies reported in the literature, a detailed theoretical description of Fe inclusions is still missing. There is even no consensual view on what kind of Fe defects take place in Fe-HAp—iron interstitial or calcium substitutions? In order to address these questions, we employ modern first-principles methodologies, including hybrid density functional theory, to find the geometry, electronic, magnetic and thermodynamic properties of iron impurities in Fe-HAp. We consider a total of 26 defect configurations, including substitutional (phosphorus and calcium sites) and interstitial defects. Formation energies are estimated considering the boundaries of chemical potentials in stable hydroxyapatite. We show that the most probable defect configurations are: Fe3+ and Fe2+ substitutions of Ca(I) and Ca(II) sites under Ca-poor conditions. Conversely, Fe interstitials near the edge of the hydroxyl channel are favored in Ca-rich material. Substitutional Fe on the P site is also a probable defect, and unlike the other forms of Fe, it adopts a low-spin state. The analysis of Fe K-XANES spectra available in the literature shows that Fe-HAp usually contains iron in different configurations.

Pure model geopolymers present a promising potential for high-temperature binders for structural or coating applications. However, their well-known chemical stability, which can reach 1400°C in the case of K-activated geopolymer, is accompanied by deleterious dimensional behavior, with significant shrinkage on heating. The work in the present paper focuses on the impact of tailored calcined argillite added to geomaterial formulations for fireproofing applications. Calcined argillite acts both as a filler and a reagent, with a supplementary delayed reaction activated by humidity and heat. K-activation of a mix of one-third metakaolin with two-thirds calcined argillite enables the shrinkage rate to be limited, and is accompanied by improved self-healing during viscous creep (allowing to preserve mechanical resistance at high temperature). This composite formulation preserves chemical stability, improves physical behavior, and maintains interesting mesoporosity for hydric properties. These different aspects are beneficial for a high temperature application.

The thermal behavior of a model MK based K‐geopolymer (Si/Al = 1.38 and K/Al = 0.68; obtained by alkaline activation of a very pure metakaolin) was investigated between room temperature and 1400°C in order to evaluate its potentiality for high‐temperature applications. The purpose of our study was to monitor the behavior of a geopolymer during a temperature rise in order to better understand its variations with respect to temperature. The works from the present paper focus only variations in the internal structure of the mineral matrix. The results presented here show that the amorphous mineral matrix is preserved up to 900°C. The results also show that there is a densification of the internal structure of tetrahedral network during heating, due to changes in the Q³ environments in fully‐connected Q⁴ for both silicates and aluminates. Thus, our work provides a new more precise vision of the 3D geopolymeric mineral matrix for which the silicoaluminous network is not exclusively composed of Q⁴ entities, contrary to what is frequently encountered in the literature before.

The thermal behavior of a model MK‐based K‐geopolymer was investigated between room temperature and 1400°C in order to evaluate its potentiality for high‐temperature applications. The purpose of our study was to monitor the behavior of a geopolymer during a temperature rise in order to better understand its variations with respect to temperature. The works from the present paper focus only changes in the porous network; it follows a first part devoted to variations in the mineral matrix. The results obtained here show that the geopolymer material preserves its porous integrity up to 800°C, while maintaining the reversibility of water exchanges corresponding to about 25 weight percent. Together with the results of part 1, the findings of this study allow us to affirm that geopolymer materials are only very little affected by temperatures up to 800°C, or even 900°C (keeping its mesoporous amorphous structure).

Calcium phosphates (CaPs) are one of the major mineral families of wide interest in biomineralization and biomaterials development. The identification and quantification of the different CaPs phases (crystalline and amorphous)...

Statement of significance: Biphasic Calcium Phosphates (BCP) are bioceramics composed of hydroxyapatite (HAp, Ca10(PO4)6(OH)2) and beta-Tricalium Phosphate (β-TCP, Ca3(PO4)2). Because their chemical and mineral composition closely resembles that of the mineral component of bone, they are potentially interesting candidates for bone repair surgery. Doping can advantageously be used to improve their biological behaviors; however, it is important to describe the doping mechanism of BCP thoroughly in order to fully appraise the benefit of the doping process. The present paper scrutinizes in detail the incorporation of copper cation in order to correctly interpret the behavior of the Cu-doped bioceramic in biological fluid. The understanding of the copper doping mechanism, related to doping mechanism of others 3d-metal cations, makes it possible to explain the rates and kinetic of release of the dopant in biological medium. Finally, the knowledge of the behavior of the copper doped ceramic in biological environment allowed the tuning of its cytotoxicity properties. The present study resulted on pre-treated ceramic disks which have been evaluated as promising biocompatible ceramic for bone substitute and/or prosthesis coating: good adherence of bone marrow cells with good cell viability.

Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) present a mineral analogy with the nano-multi-substituted hydroxyapatite bio-mineral part of bones. At the same time, doping can be used to tune the biological properties of these ceramics. This paper presents a general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature. The results enable the preparation of doped synthetic BCP that can be used to tailor biological properties, in particular by tuning the release amounts upon interaction with biological fluids. Intermediate sintering temperatures stabilize the doping elements in the more soluble β-TCP phase, which favors quick and easy release upon integration in the biological environment, whereas higher sintering temperatures locate the doping elements in the weakly soluble HAp phase, enabling a slow and continuous supply of the bio-inspired properties. An interstitial doping mechanism in the HAp hexagonal channel is observed for the six investigated cations (Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with specific characteristics involving a shift away from the center of the hexagonal channel (Fe³⁺, Co²⁺), cationic oxidation (Mn³⁺, Co³⁺), and also cationic reduction (Cu⁺). The complete crystallochemical study highlights a complex HAp doping mechanism, mainly realized by an interstitial process combined with calcium substitution for the larger cations of the series leading to potentially calcium deficient HAp.

Statement of significance: Biphasic calcium phosphates (BCPs) are bioceramics composed of hydroxyapatite (HAp, Ca10(PO4)6(OH)2) and beta-Tricalium Phosphate (β-TCP, Ca3(PO4)2). Because their chemical and mineral composition closely resembles that of the mineral component of bone, they are potentially interesting candidates for bone repair surgery. Doping can advantageously be used to improve their biological behaviors and/or magnetic properties; however, it is important to describe the doping mechanism of BCP thoroughly in order to fully appraise the benefit of the doping process. The present paper scrutinizes in detail the incorporation of ferric cation in order to correctly interpret the behavior of the iron-doped bioceramic in biological fluid. The temperature dependent mechanism has been fully described for the first time. And it clearly appears that temperature can be used to design the doping according to desired medical application: blood compatibility, remineralization, bactericidal or magnetic response.

Stability of metal-organic frameworks is one of the central issues for their successful usage in an increasingly wide range of applications. Particularly Zeolitic Imidazolate Frameworks (ZIFs) are known for their high stability. Herein we use the two most stable representatives ZIF-8 and ZIF-67 to show that the concomitant effect of pressure and temperature upon water intrusion/extrusion cycles is strikingly higher compared to the separate effects of either pressure or temperature and leads to previously unobserved irreversible structural changes. We also explore the effect of compression-decompression speed on the pronounced breathing effect of indicated ZIFs as part of high-pressure operation and show that framework relaxation time may be very long and should be taken into account for potential applications. This journal is

The present study gives a fine description of the Zn2+ location in Zn-doped Biphasic Calcium Phosphate (BCP) samples heat treated between 500 °C and 1100 °C. Structural considerations were used to explain the sample interactions with biological fluid (DMEM). X-ray Absorption Spectroscopy (XAS) experiments were used to characterize the powdered samples. The main results (1) indicate the presence of Zn2+ complexes physisorbed at the HAp surface for a sintering temperature of 500 °C, (2) confirm the insertion of Zn2+ into the β-TCP phase using a substitution mechanism for a sintering temperature around 700 °C, and (3) fully describe the insertion of Zn2+ into the HAp phase by an interstitial mechanism for heat treatment above 900 °C (composition Ca10Znx(PO4)6(OH)2−2xO2x; xmax 0.25). The formation of the linear O–Zn–O entity with dZn–O = 1.72(2) Å has been clearly evidenced by Fourier transform amplitude fitting in the R-space (Zn two-fold coordination unambiguously described for the first time). The mineralisation stimulatory effect of Zn2+ incorporated into BCP has been explained by two different mechanisms. For samples heat treated between 500 °C and 800 °C, the stimulatory effect is attributed to the presence of soluble Zn2+ species: Zn2+ physisorbed at the HAp surface for sintering treatment around 500 °C and Zn2+ incorporated into about 20 wt% (weight percent) of the soluble Zn-doped β-TCP phase for sintering treatment around 800 °C. A sintering temperature above 900 °C led to the formation of an extremely weakly soluble and well-crystallized Zn-doped HAp phase which acts by facilitating the nucleation of a calcium phosphate phase at its surface.